Revert #626 bumping gojsonschema

[silvin-lubecki]

Dependencybot only bumped the gopkg.toml and not the vendored code. It does not compile in the docker/cli code, so I prefer reverting the bump right now and fix the docker/cli code, then bump both of them.
- A picture of a cute animal (not mandatory but encouraged)

[GordonTheTurtle]

Please sign your commits following these rules:
https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work
The easiest way to do this is to amend the last commit:

$ git clone -b "fix-gojsonschema-vendoring" git@github.com:silvin-lubecki/app.git somewhere
$ cd somewhere
$ git commit --amend -s --no-edit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[glours]

LGTM

[codecov]

Codecov Report

Merging #638 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #638   +/-   ##
=======================================
  Coverage   72.14%   72.14%           
=======================================
  Files          49       49           
  Lines        2542     2542           
=======================================
  Hits         1834     1834           
  Misses        479      479           
  Partials      229      229

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